1. Field of the Invention
The disclosed embodiments relate to thermal testing systems. More specifically, the embodiments disclosed relate to processes of simulating icing conditions for the purpose of testing aircraft ice protection equipment.
2. Description of the Related Art
The ice protection equipment employed on many aircraft includes a number of heating elements deposited on an inside surface of an aircraft skin at a leading edge of a particular component, e.g., wings, horizontal tails, and other parts that are susceptible to icing. Many systems include, at the very front of the leading edge, a “parting strip” heating element, and immediately behind the parting strip, what are referred to as “shed zone” heating elements. An upper shed zone element may be located on a top surface of the leading edge slightly back from the parting strip, and a lower shed zone element may be located below and slightly back of the parting strip. Before releasing such parts for use on an aircraft, it is critical for safety and other reasons that the heating elements are tested to ensure the equipment meets the desired performance requirements and that device failure is minimized.
One defect encountered in the manufacture of aircraft wings and other similar parts can exist in what is referred to as “matting” that may be used to secure heating elements to an inside surface of the skin at the leading edge. The matting is highly thermally conductive such that it promotes heat transmission from the heating element to the aircraft skin. Problems are encountered, however, when air bubbles exist in the matting between the heating element and the aircraft skin. As is noted in the art, air is highly resistant to heat transfer, and therefore air pockets in the matting can impair heat transmission from the heating element(s), and thus can promote unacceptable ice build up at the leading edge.
The manufacturer often tests the parts in what is referred to as an “icing tunnel”—a wind tunnel that simulates icing conditions as would exist in nature. An icing tunnel typically provides forced air that is highly saturated with supercooled water droplets at a full range of temperatures below freezing. Whether the ice is effectively eliminated can be, in some instances, visualized on the part during testing, or detected in other ways such as using sophisticated measurement equipment.
Icing tunnel testing will quickly show any deficiencies in heat transmission to the leading edge skin through a combination of visual observation and instrumentation. Defects in the heater installation can result in deficiencies in heat transmission to the leading edge skin with resulting unacceptable ice protection performance.
Using icing tunnels for testing purposes with defective parts, however, can be extremely expensive. Further, this expense is exacerbated considering that a single part may require three to four tests in the icing tunnel before it is successfully cleared.